The present invention relates to an apparatus for assembling components by soldering, especially miniature IC-packages on a printed circuit board and, more particularly, to an apparatus for soldering the lead pins on an IC-package with the corresponding lead lines on a printed circuit board using radiant heat, for attaining firm and reliable connections in a short time.
Miniature IC-packages have the advantage that they permit higher package density by mounting many IC-packages on a single printed circuit board, especially in memory elements. Such a type of IC-package includes, for instance, an SOP (Small Outline Package) having lead pins extending in two directions, or an FPP (Flat Plastic Package) having lead pins extending in four directions.
As will be understood, such IC-packages tend to have their lead pins arranged in more and more dense distribution in accordance with the growing general demand for multiple functionalities of LSI.
There have been known as the means for soldering the lead pins on an IC-package to the corresponding lead lines on a printed circuit board, for example, heating with a soldering iron, heating by a pulse heater, infrared ray heating with reflowing, and heating by hot air [see, for example, "Denshi-Zairyo" (Electronics Materials) No. 2, p. 37 (1985)] and, as proposed recently, the use of laser beams ["Keikinzoku-Yosetsu" (Welding of Light Metals) Vol. 17, No. 1 (1979)]. The known techniques have, however, many drawbacks. Thus, a miniature IC-package has in general its lead pins disposed with a narrow pin pitch. In this case, positioning the lead pins in alignment with the soldering pad requires higher accuracy when the number of lead pins is large and, in addition, leads to the occurrence of electric short circuiting across the neighboring pins due to excessive application of solder, so that minute and close control of the operations and sophisticated techniques for the printing application of the solder paste and for the mounting of the IC-packages on the printed circuit board, etc., are required.
As materials for the printed circuit board, those exhibiting very low heat resistance, such as paper, phenolic resin and so on, have recently come to find practical use for the sake of economy, so that printed circuit boards are apt to suffer from thermal damage when employing, in particular, an infrared ray heating with reflowing, heating with hot air, or laser beam heating. When a laser beam is employed, stable soldering may be achieved, since there occurs no degradation of the material of the heating head with time by, for example, formation of an oxide layer and so on, as contrasted to the technique using thermal conductivity, such as the use of a soldering iron and so on. The technique of using a laser beam has, however, the disadvantage that a complicated device is necessary for positioning the optical exit member for the laser beam to be guided through a flexible fiber so as to focus the beam onto the site to be soldered. Here a part of the laser output energy will be scattered onto portions other than the sites to be soldered due to diffraction of the beam, and this injures the material (IC-packages, printed circuit board and so on), resulting in a degradation of the final product.